Intravenous high-dose vitamin C

Is it safe?

Adverse events

Vitamin C itself is essentially non-toxic. In general, adverse events after high-dose intravenous vitamin C were mild, and consistent with side effects occurring due to rapid infusion of any high-osmolarity solution, and were preventable by drinking fluids before and during the infusion.1,35,38

Contraindications

Patients with glucose 6-phosphate dehydrogenase deficiency were found to be at risk to experience haemolysis (breakdown of red blood cells) following administration of high doses of vitamin C.53,54 Therefore patients should be screened for this metabolic deficiency before initiation of therapy.

Oxalic acid is an end product of metabolic oxidation of vitamin C. Oxalate nephropathy has been reported after administration of intravenous vitamin C in subjects with renal dysfunction.55-57 However, in people with normal renal function, the risk of oxalate crystallization in the kidney was not increased.58 Therefore, high-dose intravenous vitamin C is contraindicated in people with renal dysfunction, and a history of kidney stones should be reviewed.

Interactions

As vitamin C at physiological concentrations has antioxidant properties, it is conceivable that it may attenuate the anti-cancer activity of therapies generating increased reactive oxygen species, e.g. radiation and some chemotherapeutics.

Several studies on interactions of vitamin C and anti-cancer therapies have been performed, both in vitro and in vivo.36-37,60-68 Vitamin C was found to reinforce the action of radiation and several chemotherapeutics, while it has no influence or even diminishes the effects of other chemotherapeutics. In this respect, the results of Heaney et al. are worth mentioning.69 When comparing the therapeutic efficacy of a range of anticancer agents in cell lines and tumour-bearing mice with and without pretreatment with dehydroascorbic acid (the oxidized form of vitamin C), it was found that the latter caused a dose-dependent reduction of cytotoxicity; however, later studies questioned the relevance of these findings when using pharmacological concentrations of vitamin C.63 Also, several studies showed that vitamin C could abrogate the effects of bortezomib when taken simultaneously.70

In conclusion, negative interactions may occur when adding vitamin C to conventional anti-cancer therapy, making the conventional therapy less potent.

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